March 13, 2023

Prehospital Traumatic Cardiac Arrest: A Systematic Review and Meta-analysis

Written by Dan Wolf, MD
REBEL EM
Medical Category: EMS and Disaster, Trauma

Background: Traumatic cardiac arrest in the prehospital setting carries an extremely high mortality rate. Nevertheless, mortality of prehospital traumatic cardiac arrest (TCA), and survivability with good neurologic outcome, remain the gold standards of trauma care in and out of the hospital and are effectively the criterion by which we measure outcomes in the trauma literature. In recent years, emergency response systems have made significant efforts to study, standardize, and improve the management of prehospital TCA in the field with the hopes of improving its survivability.

In this systematic review and meta-analysis, researchers aim to establish an accurate prehospital TCA mortality rate and explore associations between survivability and the many factors contributing to prehospital TCA management.

Article: Vianen NJ et al. Prehospital traumatic cardiac arrest: a systematic review and meta-analysis. Eur J Trauma Emerg Surg. 2022 Aug;48(4):3357-3372. Epub 2022 Mar 25. Erratum in: Eur J Trauma Emerg Surg. 2022 May 5. PMID: 35333932

Objectives:

What is the pooled mortality rate for prehospital TCA?
Does the inclusion of patients pronounced dead on scene and the presence of a physician-based EMS organization affect the pooled mortality rate and survival with favorable neurologic outcomes for prehospital TCA?
Are any pre- or intra-arrest factors prognostic of prehospital TCA mortality?

What They Did:

Two researchers performed a systematic review and meta-analysis following the PRISMA and CHARMS guidelines
They collected articles using Embase, Medline ALL via Ovid, Web of Science Core Collection, and Google Scholar published between 1995-2020.
The search contained terms for (1) prehospital cardiac arrest or prehospital advanced life support, and (2) injuries and trauma.
The references on all selected articles were then used to identify additional studies.
Two authors independently screened all articles and collected data; discrepancies were solved via discussion between the two authors.
An additional division was performed, separating studies from countries or regions with prehospital physician-based EMS systems vs those without.

Inclusion Criteria:

Articles written in English, French, German, or Dutch
Studies with reported outcomes of interest for prehospital TCA

Exclusion Criteria:

Any study with >10% pediatric patients
Military studies or those using combat patients
Studies only focusing on a single treatment or intervention
Animal studies
Studies whose full text was unavailable
Studies published before 1995
Conference papers and unindexed journals

Results:

The search yielded 2957 articles
- 2865 were excluded based on title or abstract
92 articles were screened for full-text review
- 56 additional articles were excluded
36 articles remained for inclusion
- All 36 articles met quality and bias standards
- Papers included data from 51,722 patient
Overall pooled TCA mortality and neurological outcome:
- 36 studies
- 96.2% (95%CI 95.0-97.2)
Overall pooled favorable neurologic outcome:
- 13 studies
- 43.5% (95%CI 32.3-55.0)
Prognostic Factors for TCA Mortality:
- Non-shockable initial rhythm was the only statistically significant prognostic factor and only in the study cohorts, including prehospital deaths.
- RR 1.12 (95% CI 1.03-1.21; p=0.006)

Strengths:

Performed an exhaustive literature search encompassing major databases, and the sources of each paper were also searched for completeness.
Used established guidelines via the PRISMA and CHARMS checklists.
Literature search and review strategy is thorough and reproducible.
Assessed the quality of papers using Newcastle-Ottawa Quality Assessment Scale.
Assess bias using the RevMan Risk of Bias Tool.
Used a patient-centered search query.
Inclusion/Exclusion criteria and definitions were very specific.
Authors included their search terminology, allowing for reproducibility.
Resultant data contained a large sample size from various countries and healthcare systems in multiple languages.

Limitations:

Patient populations in some of the included studies likely overlap, allowing some patients to be counted multiple times.
The investigators did not contact authors or subject matter experts.
The investigators did not include un-indexed journals or gray literature.
A third party did not arbitrate discrepancies in article selection.
The agreement rate between the authors was not reported.
Of the included articles, only one was a randomized controlled trial, and only two were prospective trials.
The weight of the included studies was only reported for the subgroup analysis in Figure 7.
Subgroup analysis on EMS system type and favorable neurologic status were less powered and had much wider CI ranges, making the data much less definitive.
Subcategory data on EMS system type is still extremely variable, given the range of included EMS systems and regions. It would be difficult to draw direct conclusions on a prehospital physician’s impact on traumatic cardiac arrest without much more data.
Inconsistency and lack of reporting prehospital intracardiac arrest factors limited this study’s ability to draw any conclusions on prognostic factors.
The only statistically significant factor intra-arrest was the first ECG rhythm, which only had an odds ratio of 1.12, which is relatively low.

Discussion:

Dead On Scene:

The 96.2% mortality rate and 43.5% rate of favorable neurologic outcomes in survivors are consistent with prior studies in recent years. (Grasner 2011; Zwingmann 2012) Their data pools overlap considerably with previous studies; it would have been concerning if the data differed significantly.
Intuitively, studies that exclude patients dead on scene should have much higher survivability rates and favorable neurologic outcomes. By selectively removing patients who have already achieved the worst possible outcome, those remaining will undoubtedly have better outcomes.
Studies including patients dead on scene are more epidemiologically useful, as the data likely represent true survivability and neurologic outcomes of patients involved in prehospital TCA. In contrast, data from studies that exclude prehospital deaths may be more useful to tease out intra-arrest factors leading to apparently improved outcomes.

Pre-Hospital Physician-Based EMS:

The data indicate a substantial reduction in morbidity and mortality when prehospital physicians are available. However, as the authors point out, there are many confounding variables.
Could we attribute the discrepancy to better triage where only patients thought to have a better chance of survival had prehospital physician deployment? Or, could the distinction be due directly to the usage of advanced prehospital medicine and intervention by the EMS physicians? However, we might expect on-scene advanced trauma resuscitation to prolong prehospital time sizably.
Many studies suggest that increased time spent on scene correlates with worse outcomes for trauma (Stiell 2008) and all-cause incidence (Isenberg 2005) across all levels of prehospital care.
Lastly, data collection is often limited, and many important factors are unreported. Could factors such as downtime before the arrival of EMS, time in the field, time in transit to the hospital, and trauma center vs. non-trauma center destination account for the discrepancy? These factors vary considerably between regions, countries, and even local EMS agencies. Further clarification of these uncertainties may be pivotal and warrant future exploration.

Heterogenous Population:

Heterogeneity (I2) was high between the cohorts. Therefore, we may be uncomfortable pooling the results of studies with vastly different pathologies, and as a result, it is questionable whether a meta-analysis is appropriate.
The authors attempt to delineate intra-arrest prognostic factors that could explain survivability. They analyzed eight independent factors, and “shockable first ECG rhythm” was the only statistically significant factor, and only in the studies including prehospital death, with a RR of 1.12 (95% CI 1.03-1.21; p=0.006).
Likewise, other studies in both traumatic and nontraumatic cardiac arrest (Tran 2020) report comparable findings.
However, the data do not provide a deeper understanding or allow for creating an actionable plan for the resuscitation of TCA patients. More research is needed to define what factors could provide significant insights into the survivability of prehospital TCA patients.

Author’s Conclusion: “In conclusion, prehospital TCA is associated with a high mortality rate, with approximately one in twenty patients surviving to discharge. When interpreting results from studies on this subject, factors such as the in- or exclusion of patients that have deceased on-scene and the type of prehospital EMS system (physician-based) should be considered. Apart from the first monitored ECG rhythm, this study found no other prognostic factors available to differentiate between survivors and non-survivors.”

Clinical Bottom Line:

Prehospital TCA has a high mortality and low favorable neurologic outcomes. Before extrapolating data from prehospital studies, it is essential to discern whether patients declared dead on the scene were included, as the results can vary widely. Furthermore, a physician-based EMS system may or may not impact prehospital TCA mortality and favorable neurologic outcomes in survivors. But, further study is needed to identify precisely how physicians benefit TCA patients. Lastly, shockable first ECG rhythm remains a prognostic factor in prehospital TCA, and more data is needed to identify additional intra-arrest factors.

References:

Grasner JT, et al. Cardiopulmonary resuscitation traumatic cardiac arrest—there are survivors. An analysis of two national emergency registries. Crit Care. 2011;15(6):276. PMID: 22108048
Zwingmann J, Mehlhorn AT, Hammer T, Bayer J, Südkamp NP, Strohm PC. Survival and neurologic outcome after traumatic out-of-hospital cardiopulmonary arrest in a pediatric and adult population: a systematic review. Crit Care. 2012 Jul 6;16(4):R117. PMID: 22770439
Stiell IG, Nesbitt LP, Pickett W, Munkley D, Spaite DW, Banek J, Field B, Luinstra-Toohey L, Maloney J, Dreyer J, Lyver M, Campeau T, Wells GA; OPALS Study Group. The OPALS Major Trauma Study: impact of advanced life-support on survival and morbidity. CMAJ. 2008 Apr 22;178(9):1141-52. PMID: 18427089
Isenberg DL, Bissell R: Does advanced life support provide benefits to patients?: A literature review. Prehospital Disaster Med. 2005, 20: 265-70. PMID: 16128477
Tran A, et al. Pre-arrest and intra-arrest prognostic factors associated with survival following traumatic out-of-hospital cardiac arrest—a systematic review and meta-analysis. Resuscitation. 2020;153:119–35. PMID: 32531405

Guest Post By:

Dan Wolf, MD
PGY-1, Emergency Medicine Resident
Vassar Brothers Hospital, Poughkeepsie, New York
E-mail: daniel.wolf@nuvancehealth.org

Marco Propersi, DO FAAEM
Vice-Chair, Emergency Medicine
Vassar Brothers Hospital, Poughkeepsie, New York
Twitter: @marco_propersi

Post-Peer Reviewed By: Salim R. Rezaie, MD (Twitter: @srrezaie), Anand Swaminathan, MD (Twitter: @EMSwami)

Cite this article as: Dan Wolf, MD, "Prehospital Traumatic Cardiac Arrest: A Systematic Review and Meta-analysis", REBEL EM blog, March 13, 2023. Available at: https://rebelem.com/prehospital-traumatic-cardiac-arrest-a-systematic-review-and-meta-analysis/.